PROJECT SUMMARY/ABSTRACT Reduced fetal growth has been implicated in a broad range of adverse health outcomes. Growing evidence suggests that toxic metal exposures adversely affect fetal growth, indicated by reduced fetal ultrasound measurements and lower birth weight. Although most individuals are exposed simultaneously to multiple metals, which may act additively or synergistically to reduce fetal growth, the majority of studies have focused on the toxicity of individual metals. While the mechanisms underlying metal-induced reductions in fetal growth are incompletely understood, there is evidence that epigenetic dysregulation, including altered microRNA (miRNA) expression, contributes to these effects. In addition to epigenetically regulating gene expression, maternal circulating miRNAs play important roles in maternal-placental-fetal crosstalk. However, the potential role of maternal circulating miRNAs in mediating metal mixture effects on fetal growth is unknown. The goal of the proposed project is to examine the impact of prenatal metal mixture exposures on fetal growth and to determine whether altered maternal circulating miRNAs mediate these relationships. During the mentored K99 phase of this award, Dr. Howe will leverage existing data and biospecimens from 500 mother-newborn pairs in the Maternal and Developmental Risks from Environmental and Social Stressors (MADRES) study, a low- income predominately Hispanic pregnancy cohort based in Los Angeles, to investigate potential additive and synergistic relationships between prenatal exposure to 15 metals and in utero growth and birth weight. To accomplish this, she will expand metals exposure assessment in the MADRES pregnancy cohort and train in methods for analyzing complex environmental mixtures, including weighted quantile sum regression and Bayesian kernel machine regression. During the R00 phase, Dr. Howe will determine whether maternal circulating miRNAs mediate metal mixture-fetal growth relationships, using structural equation models, and will examine potential downstream effects by profiling mRNA expression levels within the maternal-placental-fetal axis, using RNA-Seq, in a subset (N = 50) of mother-newborn pairs. Results from the proposed studies may be used to improve the efficacy of public health interventions aimed at preventing metal-induced reductions in fetal growth. Furthermore, they will increase knowledge of a potential underlying mechanism (altered maternal circulating miRNAs) and may lead to the identification of early and relatively non-invasive biomarkers of metal mixture exposures and reduced fetal growth. Dr. Howe has assembled a mentoring team, spanning the University of Southern California, Boston University, and Emory University, with expertise in metals toxicity, environmental mixtures modeling, epigenetic epidemiology, and perinatology. This team will provide ongoing feedback and on-site training opportunities to complement coursework, workshops, and seminars, which will support Dr. Howe?s transition to become an independent investigator with a research program that focuses on the effects of early life metal mixture exposures on the epigenome and fetal growth.